Color diffusion transfer process utilizing ultraviolet light absorbers



Aug. 12, 1969 H. 5. ROGERS 3,

COLOR. DIFFUSION TRANSFER PROCESS UTILIZING ULTRAVIOLET LIGHT ABSORBERSOriginal Filed Jan. 14, 1959 2 SUPPORT {LAYER CONTAINING |4 ACOLOR-PROVIDING SUBSTANCE l PHOTOSENS TIvE ELEME'NOT 16 PHOTOSENS'TNELAYER PROCESSING soLUTIoN 20 T LAYER CONTAINING AN I. I 033K033:(3101 1331 I XQIK X'I K :331 31g 32 ULTRAVIOLET LIGHT ABSORBER IMAGE-RECEIVINGELEMENT 3O DYEABLE IMAGE- 34 RECEIVING STRATUM 36 SUPPORT STRATUMINVENTOR.

ATTORNEYS United States Patent Office 3,460,942 Patented Aug. 12, 19693,460,942 COLOR DIFFUSION TRANSFER PROCESS UTILIZ- ING ULTRAVIOLET LIGHTABSORBERS Howard G. Rogers, Weston, Mass, assignor to PolaroidCorporation, Cambridge, Mass :1 corporation of Delaware Continuation ofapplication Ser. No. 354,963, Mar. 26, 1964, which is acontinuation-in-part of application Ser. No. 786,766, Jan. 14, 1959.This application May 31, 1968, Ser. No. 744,595 The portion of the termof the patent subsequent to Dec. 18, 1979, has been disclaimed Int. Cl.G03c 5/54, 7/00, 1/40 US. CI. 9629 4 Claims ABSTRACT OF THE DISCLOSUREThe present invention is concerned with the protection of dye imagesformed by color diffusion transfer processes by effecting transfer to animage-receiving layer through an alkali-permeable polymeric layercontaining a nonditfusible ultraviolet light absorber.

This application is a continuation of application Ser. No. 354,963 filedMar. 26, 1964, now abandoned, which in turn is a continuation ofapplication Ser. No. 786,766 filed Ian. 14, 1959, now abandoned.

The present invention relates to color photography and more particularlyto novel photographic processes.

One object of this invention is to provide novel photographic processeswhich produce color transfer images which have enhanced resistance tosunlight.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the processes involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein FIGURE 1 is adiagrammatic enlarged sectional view illustrating the association ofelements during one stage of a preferred process of this invention, thethickness of the various materials being exaggerated.

The present invention is particularly related to color diffusiontransfer processes. In such processes a photosensitive element includinga silver halide emulsion layer is exposed and developed. Concurrent withand under the control of this development, an imagewise distribution ofmobile organic color-providing substances is formed. At least a portionof these color-providing substances is transferred to a superposedimage-receiving stratum to form a colored image thereon. As examples ofsuch processes, mention may be made of the processes disclosed andclaimed in US. Patent No. 2,983,606, issued May 9, 1961 to Howard G.Rogers, wherein dye developers (i.e., compounds which contain in thesame molecule both the chromophoric system of a dye and also a silverhalide developing function) are the color-providing substances; theprocesses claimed and disclosed in US. Patent No. 2,647,049, issued July28, 1953 to Edwin H. Land, wherein color developers are employed todevelop the latent image and color couplers are the color-providingsubstances; and the processes disclosed in US. Patent No. 2,774,668,issued Dec. 18, 1956 to Howard G. Rogers, wherein complete, prefromeddyes are used as the colorproviding substances. By the term organiccolor-providing substances, as used herein, is meant dyes, including dyedevelopers, and dye intermediates, e.g., color couplers.

In an especially useful mode of carrying out color diffusion transferprocesses such as described above, the color-providing substances aredisposed in a separate alkali-permeable layer in the photosensitiveelement. The separate alkali-permeable layer may be placed either infront of or behind the photosensitive emulsion with which it isassociated; however, in a preferred embodiment it is placed behind,i.e., on the side of the emulsion which is most distant from thephotographed subject when the emulsion is exposed, and preferably alsoadapted to be most distant from the image-receiving element when insuperposed relationship therewith. In carrying out the processes, thephotosensitive element is exposed and wetted with an aqueous alkalineprocessing solution, for example, by immersing, coating, spraying,flowing, etc., in the dark, and the photosensitive element issuperposed, prior to, during or after Wetting, on an image-receivingelement. In a preferred embodiment the aqueous alkaline processingsolution contains a viscosity-increasing compound and is applied to thephotosensitive element in a substantially uniform layer as thephotosensitive element is brought into superposed position with theimage-receiving element. The alkaline aqueous processing solutionpermeates the photosensitive emulsion and alkalipermeable layers andsolubilizes the color-providing substances to provide a substantiallyuniform distribution of the color-providing substances therein. Animagewise distribution of mobile color-providing substances is formed inundeveloped areas as a function of development. At least a portion ofthe mobile color-providing substances is transferred to and imbibed onthe dyeable stratum of the image-receiving element to form the transferimage. The image is viewed by stripping the image-receiving element fromthe photosensitive element.

Sometimes in the processes generally described above, the color-fastnessof the transfer image, upon continued exposure to sunlight, leavessomething to be desired.

The present invention is concerned with providing means for protectingsuch dye images through the use of ultraviolet light absorbers, withoutrequiring subsequent coating operations.

In a preferred mode of carrying out this invention, it has been foundthat, prior to processing, an ultraviolet light absorber may beincorporated in a layer over the dyeable stratum of an image-receivingelement and, during processing, that a substantial portion of thetransferred color-providing substances may be caused to permeate throughsuch a layer to the underlying dyeable stratum to form a color imagewhich is protected from the deleterious effects of sunlight by theultraviolet light absorber in the overlying layer.

Referring now to FIG. 1, there is shown the association of elementsduring one stage of a preferred method of carrying out the presentinvention. In FIG. 1 there is provided a photosensitive element 10, animage-receiving element 30, and a layer of processing composition 20.

The photosensitive element 10 comprises a support 12, which in turn hasbeen coated with a layer 14 containing a color-providing substance, anda photosensitive layer 16, e.g., a silver halide emulsion layer. Theimage-receiving element 30 comprises a base layer 36, a dyeableimagereceiving stratum 34 and a layer 32 containing an ultraviolet lightabsorber. In a preferred modification, the processing composition 20comprises an aqueous alkaline solution and preferably contains aviscosity-increasing material such as sodium carboxymethyl cellulose,hydroxyethyl cellulose, etc. As examples of alkaline materials which maybe present in the processing composition, mention may be made of sodiumhydroxide, sodium carbomate, and diethylamine. In some cases it may alsocontain color-providing substances, developing agents, and conventionalphotographic reagents such as accelerators, restrainers, etc. Forexample, as disclosed in the aforementioned U.S. Patent No. 2,983,606,the color-providing substance (in this case the dye developer) may bepresent initially in the processing composition in lieu of being presentin a layer in the photosensitive element, as illustrated herein in thedrawing.

According to the present invention, a photosensitive element is exposedand wetted in the dark with the processing solution 20 and thephotosensitive element 10 is superposed, prior to, during, or after saidwetting, on the image-receiving element 30, as shown in FIG. 1. Theprocessing solution permeates the photosensitive element 10 and animagewise distribution of mobile color-providing substances is formed asa function of development. At least a portion of the mobilecolor-providing substances is transferred to the image-receiving element30. The transferred color-providing substances permeate through layer 32so that a substantial portion of them are deposited on the dyeableimage-receiving stratum 34 where they are protected from the deleteriouseffects of sunlight by layer 32. Imbibition periods of approximately oneminute have been found to give good results; however, this contactperiod may be varied, where necessary, to compensate for variation intemperature or other conditions. After completion of the imbibitionperiod, the transfer image may be viewed by stripping theimage-receiving element from the photosensitive element 10.

In order that a substantial portion of the color-providing substancesmay be permeated through the layers containing the ultraviolet lightabsorbers, it is required that the polymers which are used as thecarriers for such layers be permeable to the processing solution whichis employed. As mentioned previously, such solutions are preferably ofan aqueous alkaline nature; however, in certain instances they maycontain water-miscible organic solvents such as ethanol, methanol,tetrahydrofuran, etc. When the term alkali-permeable is used to describethe polymers which are used as the carriers for the ultraviolet lightabsorber, it should be understood that said term refers to polymerswhich are permeated by aqueous alkaline solutions. It should be furtherunderstood that the aqueous alkaline solutions may containwater-miscible organic solvents such as mentioned above.

It is further desirable for good permeation that the polymers have a lowaflinity for the particular color-providing substances employed and atleast that they have a lower aflinity for the color-providing substancesthan the polymers which are used for the dyeable stratum of theimage-receiving element. The preferred polymers are those which aresubstantially nondyeable by the colorproviding substances. As will beunderstood, the afiinity of the polymers will vary depending upon thecolor-providing substances employed. Suitable polymers, having lowaflinity for the color-providing substances, may be readily selected bysimple dyeability tests which are well known to the art, e.g., a film ofthe polymers is dipped in a bath of the color-providing substance,washed, and observed for retained dye. When dye developers are empolyedas the color-providing substances, mixtures of cellulose acetatehydrogen phthalate and cellulose acetate have been found to beparticularly useful as carriers. As examples of other polymerscontemplated to be useful as carriers for the ultraviolet lightabsorbers, mention may be made of polyvinyl, sulfoandcarboxy-substituted benzals of polyvinyl alcohol, copolymers of N,N-diethylacrylamide and acrylic acid, copolymers of N,N- diethylacrylamideand acrylamide, and copolymers of dimethylarninoethyl-methacrylate andmethacrylic acid. It should be understood that mixtures of polymers maybe used to provide layers having the desired properties.

The permeation of the color-providing substances through the outerultraviolet light absorber layers may be further facilitated byincorporating mordants for the color-providing substances in theunderlying dyeable image-receiving stratum so that such stratum will bepreferentially dyed. A further means of facilitating premation comprisesincorporating precipitating agents for the color-providing substances inthe dyeable stratum. When the color-providing substances are dyedevelopers, oxidizing agents such as benzoquinones may be used to bringabout precipitation.

When hydrophilic, alkali-permeable polymers are used as carriers for theultraviolet light absorbers, small amounts of hydrophobic polymers,e.g., cellulose acetate, cellulose nitrate, may be added to such layersto reduce their water sensitivity. In certain instances, depending uponthe color-providing substances employed, such hydrophobic polymers maybe further used to reduce the dyeability of such layers. The amountadded usually may be varied to suita particular needs. Generally, aboutthree parts of the hydrophobic polymer to about eight parts of thehydrophilic polymer have been found to be particularly useful.

Ultraviolet light absorbers for use in this invention may be selectedfrom the many compounds of this nature which are commercially available.The amount of ultraviolet light absorber used will vary with manyfactors such as the efficiency of the ultraviolet light absorber itself,the original color-fast-ness of the color-providing substances, theamount of sunlight the transfer image will be exposed to during its lifeexpectancy, etc. Generally, about one part of the ultraviolet lightabsorber to about five parts of the carrier have been found effective inenhancing the color-fast'ness of the images.

As an example of a class of ultraviolet light absorbers which have beenfound to be especially useful in the processes and products of thisinvention, mention may be made of the thiazolidine ultraviolet lightabsorbers disclosed in U.S. Patent No. 2,808,330, and particularly thosehaving substituents rendering them substantially nonditfusible. Suchultraviolet light absorbers may be represented by the formula:

wherein R represents a hydrogen atom, an alkyl or an aryl group, R is anaryl group and Q is a divalent nonmetallic atom (e.g., oxygen, sulfur)or radical (e.g., imino). As an example of an ultraviolet light absorberwithin this class and which is insoluble in aqueous alkaline solutions,mention may be made of 5-benzilidene-3-hexadecyl-Z-phenylimino-4-thiazolidone.

As examples of other useful ultraviolet light absorbers, mention may bemade of those described and claimed in the copending applications ofNorman W. Schuler, Ser. No. 301,958 filed Aug. 14, 1963, now U.S. Patent3,330,- 656 and 319,693 filed Oct. 29, 1963, now U.S. Patent 3,183,219,and in the copending application of Howard C. Haas, Ser. No. 319,653filed Oct. 29, 1963, now U.S. Patent 3,330,680. The polymericultraviolet light absorbers described and claimed in these applicationsmay be employed alone or with a polymeric carrier such as heretoforedescribed.

The ultraviolet light absorbers employed may be soluble or insoluble inthe photographic processing solutions. Ultraviolet light absorbers whichare insoluble in such solutions are especially useful in that they arenot dissolved during the permeation step and remain over the dyeablestratum of the image-receiving element. It should be understood thatwhen such insoluble ultraviolet light absorbers are used, they aredisposed in polymeric layers which are permeated but not solubilized bythe processing solutions. When ultraviolet light absorbers which aresoluble in the photographic processing solutions are used, at

least a portion of the ultraviolet light absorber is dissolved by theprocessing solution during processing and deposited on the dyeablestratum of the image-receiving element along with the color-providingsubstances. Since the ultraviolet light absorbers are dissolved duringprocessing, the polymeric layer, in which they are disposed, may or maynot be soluble in the processing solution. In order that the solubleultraviolet light absorber will be preferentially deposited on thedyeable stratum, it is desirable, when selecting ultraviolet lightabsorbers, to select those which have an afiinity for the particulardyeable stratum which is to be used. It is further desirable inselecting soluble ultraviolet light absorbers to select those which havea lower rate of mobility than the color-providing substances so thatthey will tend to be deposited over the color-providing substances onthe dyeable stratum.

The image-receiving elements, over which the ultraviolet light absorberlayers are coated, generally comprise a sheet of dyeable material, e.g.,baryta. In a preferred embodiment, such elements comprise a supportwhich in turn has been coated with an image-receiving stratum of adyeable material. As examples of dyeable materials which have been founduseful for the image-receiving stratum, mention may be made of gelatin,a mixture of polyvinyl alcohol and polyvinyl pyrrolidone, a mixture ofpolyvinyl alcohol or gelatin and poly-4-vinylpyridine, copolyrners ofvinyl alcohol and vinyl pyrrolidone, and nylons such as N-methoxymethylpolyhexamethylene adipamide.

The ultraviolet light absorber layers may be applied to theimage-receiving elements from suitable coating solutions, using coatingtechniques well known to the art. The concentrations of the coatingsolutions can usually be varied to suit particular needs. Generally,coating solutions comprising 2 to 5% solids have been found to beparticularly useful. The preferred solvents for use in the coatingsolutions are those which are solvents for both the ultraviolet lightabsorber and the polymeric carrier. By using such solvents, theultraviolet light absorber is molecularly dispersed in the resultinglayer and thus provides the most effective coverage.

The products and processes of this invention are especially useful whendye developers are the color-providing substances. Dye developers, asnoted above, are compounds which contain in the same molecule both thechromophoric system of a dye and also a silver halide developingfunction. By a silver halide developing function is meant a radicalwhich is capable of developing an exposed silver halide image. In apreferred embodiment, the silver halide developing function in suchcompounds is provided by the presence of a benzenoid developing radicaltherein, e.g., a hydroquinonyl radical. Ex amples of representative dyedevelopers are given in the previously mentioned U.S. Patent No.2,983,606.

In color diffusion transfer processes employing dye developers, the dyedeveloper, as mentioned previously for color-providing substances ingeneral, is preferably but not necessarily placed in a separatealkali-permeable layer behind the photosensitive layer. Upon processing,the aqueous alkaline processing solution permeates to the separatealkali-permeable layer and solubilizes the dye developer therefrom. Asthe process proceeds, the exposed silver halide in the photosensitiveelement is developed and, as a result of this development, the dyedeveloper in the exposed areas is oxidized and substantiallyimmobilized. At least a portion of the unreacted dye developer isimbibed on a superposed image-receiving layer to create thereon thepositive dye image. In such processes the immobilization of the dyedevelopers in the exposed areas is apparently due, at least in part, toa change in the solubility characteristics of the dye developer uponoxidation. It may also be due in part to a tanning effect on theemulsion by the oxidized developer and in part to localized exhaustionof alkali due to development.

The following nonlimiting example illustrates the preparation of animage-receiving element within the scope of this invention.

Example An image-receiving element was prepared by successively coatinga cellulose acetate-coated baryta paper with the following coatingsolutions:

(1) An ethanol solution comprising 4% of N-methoxymethylpolyhexamethylene adipamide, and

(2) A tetrahydrofuran-methanol solution (1 to l, by volume) comprising2.0% cellulose acetate hydrogen phthalate, 0.75% cellulose acetate and0.5% of S-benzilidene-3-hexadecyl-2-phenylimino-4-thiazolidone.

A photosensitive element for use with the above imagereceiving elementmay be prepared, for example, by successively coating agelatin-subcoated cellulose acetate support with a solution comprising amethanol-tetrahydrofuran solution (1 to 1, by volume) comprising 3% 0f2-[p-(2',5'-dihydroxyphenethyl)-phenylazo] 4 n-propoxy-l-naphthol and 2%of a sodium sulfobenzal of p lyvinyl alcohol, followed, after drying, bya silver iodobromide emulsion coating.

The above photosensitive emulsion may be processed, after exposure, byspreading a processing solution such, for example, as an aqueoussolution comprising:

Percent Sodium carboxymethyl cellulose 5.0 Sodium hydroxide 3.0l-phenyl-3-pyrazolidone 1.2 -nitrobenzimidazole 0.122,5-bis-ethyleneiminohydroquinone 0.9

between said photosensitive element and the image-receiving element assaid elements are brought into superposed relationship. After animbibition period of approximately one minute, the image-receivingelement is separated and contains a dense magenta positive dye image ofthe photographed subject.

The effectiveness of the image-receiving elements of this invention wastested by exposing such elements, after transfer, to a bank of sun lampsalong with a control, prepared as above, in absence of the ultravioletlight absorber layer. After an exposure of seventy-two hours, thetransfer images, prepared by using the image-receiving elements of thisinvention, were substantially more stable than the control images.

Although the use of the image-receiving element was demonstrated above,using a dye developer, it is to be understood that this was for purposesof illustration only and that other color-providing substances may beused. It should be further understood that the image-receiving elementsof this invention are equally useful in multicolor diffusion transferprocesses. As examples of photosensitive elements useful in suchprocesses, mention may be made of the elements disclosed in thepreviously mentioned U.S. Patents Nos. 2,647,049 and 2,983,606, as Wellas those disclosed in the copending application of Edwin H. Land andHoward G. Rogers, Ser. No. 565,135, filed Feb. 13, 1956.

The image-receiving elements of this invention are especially useful incomposite roll film units intended for use in a Polaroid Land Camera,sold by Polaroid Corporation, Cambridge 39, Mass, or a similar camerastructiire such, for example, as the camera forming the subject matterof U.S. Patent No. 2,435,717, issued to Edwin H. Land on Feb. 10, 1948.In general, such composite roll film units comprise a photosensitiveroll, a roll of image-receiving material and a plurality of podscontaining an aqueous alkaline processing solution. The rolls and podsare so associated with each other that, upon processing, thephotosensitive element may be superposed on the image-receiving elementand the pods may be ruptured to spread the aqueous alkaline processingsolution between the superposed elements. The nature and construction ofthe pods used in such units are well 7 known to the art. See, forexample, U.S. Patents Nos. 2, 543,181 and 2,634,886, issued to Edwin H.Land.

It has also been found that, in lieu of being present initially in alayer overlying the image-receiving stratum, the ultraviolet lightabsorber may be suppiled to the processing composition and depositedalong with the colorproviding substances on the image-receiving stratum.The ultraviolet light absorber may be initially placed in the processingsolution itself or it may be placed in the photosensitive element andsolubilized therefrom during processing. The ultraviolet light absorbersused in this mode of the invention should be soluble in the aqueousalkaline processing solutions and should be inert in any reactions towhich the color-providing substances may be subjected, e.g., colorcoupling. When the ultraviolet light absorber is initially placed in theprocessing solution, best results are obtained when measures are takento prevent the ultraviolet light absorbers from being prematurelydeposited on the image-receiving stratum. On such measure is to use asthe image-receiving stratum a material which has a slower rate ofpermeation by the processing solution than the materials used in thephotosensitive elements.

When the ultraviolet light absorbers are initially disposed in thephotosensitive elements, they may be incorporated in various positionsthroughout such elements. In a preferred embodiment, the ultravioletlight absorber is incorporated in a separate alkali-permeable layeralong with the color-providing substances. Upon processing, theultraviolet light absorber is solubilized by the processing solution andtransferred along with the imagewise distribution of color-providingsubstances to the image-receiving layer. The preferred ultraviolet lightabsorbers for use in this embodiment have rates of mobility in theprocessing solution such that they will not be transferred before thecolor-providing substances.

In another useful embodiment, the ultraviolet light absorber is disposedin a separate alkali-permeable layer apart from the color-providingsubstance in the photosensitive element. The layer bearing theultraviolet light absorber is preferably placed behind the layercontaining the color-providing substances so that during processing theultraviolet light absorber will be dissolved after the color-providingsubstances and tend to be deposited over them on the image-receivingstratum. In a further embodiment, the separate alkali-permeable layercontaining the ultraviolet light absorber may be applied over thephotosensitive emulsion. This embodiment is especially useful when anultraviolet light absorber is used which has a lower rate of mobilitythan the color-providing substance. This embodiment is particularlyadvantageous in that the ultraviolet light absorber layer can performother useful functions in addition to protecting the transferredcolorproviding substance. One such function would be to act as a hazefilter and antiabrasion coat for the photosensitive emulsion. Anothersuch function would be to decrease the etfect of ultraviolet light onblue-sensitive emulsions when such emulsions have excessive ultravioletsensitivity. It would be further useful in multicolor, multilayerphotosensitive elements and especially in those wherein a yellow filteris placed behind a bluesensitive emulsion and it is desirable to cutdown the amount of ultraviolet light transmitted to the red and greenlayers. In a still further embodiment, an ultraviolet light absorber maybe placed in the photosensitve emulsion stratum. Since in some casesultraviolet light absorbers may tend to desensitize the photosensitivematerial, suitable precautions should be taken in selecting theultraviolet light absorber to be so used.

In still another embodiment, a transparent image-receiving element isemployed and an ultraviolet light absorber is disposed in the supportingstratum of said element. Upon processing, the color-providing substancesare transferred to the dyeable stratum of the image-receiving elementand an opaque background, preferably white, is provided behind thedyeable stratum so that the transfer image is viewed through the supportby reflection. The opaque background behind the dyeable stratum may beprovided by various methods. As an example of one such method, mentionmay be made of a thin, permeable layer, e.g., containing a white pigmentsuch as titanium dioxide, located over the dyeable stratum and throughwhich the color-providing substances difiuse to the dyeable stratum. Usealso may be made of the processes disclosed in U.S. Patent No.2,647,056, wherein an opacifier is incorporated in the viscousprocessing solution and the processing solution is adapted so as topreferentially adhere to the image-receiving stratum. Another mode ofproviding an opaque background comprises incorporating a material in theprocessing solution and another material on the surface of theimage-receiving stratum which, when reacted with the former material,produces an opaque product. An example of this method may be found inU.S. Patent No. 2,607,685, wherein sodium carbonate is used in theprocessing solution and zinc hydroxide is incorporated in theimage-receiving stratum. It should be understood that the opacifiers oropacifying reagents may be incorporated in separate processing solutionswhich are distinct from those used to process the photographic image.When it is desirable to use such separate solutions, film units whichcontain a plurality of rupturable reagent containers, such as thosedisclosed in the above-mentioned U.S. Patent No. 2,607,685, may beemployed. In a further mode of providing an opaque background, theimage-receiving element may be superposed on and adhered to an opaquesheet after processing.

The images produced in the above embodiment will appear reversed whenviewed through the support. In most instances this reversal will not beobjectional but, if it is desirable to remedy it, one may use a camerawhich contains an odd number of mirrors in the focal path between thelens and the photosensitive element. Examples of such cameras may befound in U.S. Patent No. 2,834,269.

In cases where the ultraviolet light absorbers exhibit color changes inan alkaline medium, provisions may be made to provide that theimage-receiving element, after processing, will have a suitable pH torender such ultraviolet light absorber substantially colorless. One suchprovision would be to use a volatile alkaline material in the processingcomposition so that after processing it would volatilize from theimage-receiving element and reduce the pH of said element. As examplesof volatile alkaline materials, mention may be made of diethylamine,ethylamine, ethanolamines, etc. Another useful provision which may beused would be to incorporate an acid into the image-receiving elementwhich would neutralize any alkaline material which may be depositedthereon during processing. As examples of suitable acids, mention may bemade of citric acid, oxalic acid, etc. A particularly useful method ofcontrolling the pH of the imagereceiving element is the use of apolymeric acid layer, as disclosed and claimed in the copendingapplication of Edwin H. Land, Ser. No. 234,864, filed Nov. 1, 1962, andnow U.S. Patent 3,362,819.

A particularly useful class of ultraviolet light absorbers are thosewhich are phototropic, i.e., ultraviolet light absorbers which aresubstantially colorless when not absorbing ultraviolet radiation andwhich are activated when strongly irradiated by ultraviolet radiation.Although such phototropic ultraviolet light absorbers may become coloredwhen activated by strong ultraviolet radiation, they revert to thecolorless form when such radiation is removed.

The concept of applying the ultraviolet light absorber to the processingcomposition in lieu of having it initially in a layer over the dyeableimage-receiving stratum, e.g., layer 32 overlying layer 34 of thedrawing, is described and claimed in copending application Ser. No.247,866

9 filed Dec. 28, 1962, now U.S. Patent 3,249,435 which in turn is acontinuation-in-part of application Ser. No. 786,766 filed Jan. 14,1959, now abandoned.

Since certain changes may be made in the above processes withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:

1. In a process of forming a photographic image in color wherein anexposed silver halide emulsion is developed in the presence of at leastone dye developer to provide an imagewise distribution of mobile dyedeveloper, said dye developer being a compound which is both a dye and asilver halide developing agent, and said imagewise distribution ofmobile dye developer is transferred to a superposed image-receivingstratum to produce a transfer image thereon, the improvement whereinsaid transfer is effected to an image-receiving element having anultraviolet light absorber in an alkali-permeable polymeric stratum overthe dyeable image-receiving stratum and transferring a substantialportion of the said mobile dye developer through said polymeric stratumto said dyeable image-receiving stratum, said polymeric stratum havingless afiinity for the said dye developer than the imagereceivingstratum, said polymeric stratum comprising an alkali-insoluble polymerand said ultraviolet light absorber being nondifiusible.

2. In a process of forming a color transfer image by diffusion transfer,wherein a photosensitive element comprising an exposed silver halideemulsion is developed by an aqueous alkaline solution in the presence ofa dye developer, said dye developer being a compound which is both asilver halide developing agent and a dye, and an imagewise distributionof diffusible, unoxidized dye developer is formed in undeveloped areasof said exposed silver halide emulsion as a function of development, andat least a portion of said imagewise distribution of dye developer istransferred by diffusion to an image-receiving element including animage-receiving layer to provide said color transfer image, and saidimage-receiving element is separated from its superposed relationshipwith said silver halide emulsion, the improvement wherein saidimage-receiving element includes an alkali-permeable polymeric stratumcontaining an alkali-insoluble ultraviolet light a-bsorber positionedover said image-receiving layer, said polymeric stratum having asubstantially lower affinity for said unoxidized dye developer than doessaid image-receiving layer whereby said unoxidized dye developertransfers through said polymeric stratum to said image-receiving layer,and said alkali-permeable polymeric stratum remains adhered to saidimage-receiving layer when said image-receiving element is separatedfrom said photosensitive element.

3. A process as defined in claim 2 wherein said ultraviolet lightabsorber comprises a nondiffusible thiazolidine ultraviolet lightabsorber.

4. A process as defined in claim 2 wherein said nondiffusibleultraviolet light absorber comprises a polymeric ultraviolet lightabsorber in an alkali-permeable polymeric carrier.

References Cited UNITED STATES PATENTS 2,808,330 10/1957 Sawdey 96842,882,150 4/1959 Van Allen et al. 96--84 2,888,346 5/1959 Tulagin et al.9684 3,069,262 12/1962 Haas 96-29 I. TRAVIS BROWN, Primary Examiner U.S.Cl. X.R. 96-3, 77, 84

